Tank For A Reducing Agent, Motor Vehicle Having A Tank For A Reducing Agent And Method For Operating An SCR System Of A Motor Vehicle

ABSTRACT

A tank for a reducing agent which forms ammonia or which includes ammonia, has a planar first tank volume and at least one elongate second tank volume. A motor vehicle has an internal combustion engine, an exhaust system with an SCR catalytic converter and a reducing agent metering device and a body with a roof. A tank with a planar first tank volume for the reducing agent is provided on the roof. A method for operating an SCR system of a motor vehicle which has at least two tank volumes, a reducing agent metering device and an SCR catalytic converter, is also provided.

CROSS-REFERENCE TO RELATED APPLICATION

This application claims the priority, under 35 U.S.C. §119, of GermanPatent Application DE 10 2008 022 515.0, filed May 7, 2008; the priorapplication is herewith incorporated by reference in its entirety.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a tank for a reducing agent. The tankhas a planar first tank volume and at least one elongate second tankvolume. The invention also relates to a motor vehicle having a tank fora reducing agent and to a method for operating an SCR system of a motorvehicle having at least two tank volumes for a reducing agent.

Due to the increased demands on the exhaust-gas purification systems ofinternal combustion engines, in particular of diesel engines,ever-increasing use is made of SCR systems in the exhaust systems ofinternal combustion engines in order to reduce the nitrogen oxides in anexhaust gas. In that case, the exhaust-gas or emissions regulationswhich have now been agreed to in many countries apply not only toon-road vehicles such as passenger vehicles and utility vehicles, butalso apply even today, or will apply in the near future, to so-calledoff-road vehicles, that is to say for example to tractors and otheragricultural vehicles.

In addition to the integration of such SCR systems during thedevelopment phase of vehicles, SCR systems which can be retrofitted inparticular are of great significance, because the purchase costs ofoff-road vehicles are generally very high.

The retroactive integration of such SCR systems is generally difficultsince the tank capacities for the reducing agent of an SCR system mustbe selected to be very large in order to obtain the longest possibleservice intervals and due to intensive utilization of the vehicles.Furthermore, in particular in agricultural machines, for example intractors, there are many restrictions with regard to installationlocation, because the visibility of the front region in front of thebody is particularly significant.

Furthermore, the system components of such an SCR system should beconstructed to be very light with regard to their weight, and shouldhave a low level of complexity with regard to freedom from maintenance.Furthermore, the production and operating costs must be reduced and, inparticular, the least possible amount of additional energy of theinternal combustion engine or of the electrical energy accumulator orenergy generator should be consumed. In the case of a retroactiveinstallation of such an SCR system into a motor vehicle, themodification measures required should also be as minor as possible.

From the above statements, it is clear that there are numerousrequirements for the (retroactive) installation of SCR systems in motorvehicles in order to ensure long service lives and service intervals ofthe vehicle and to generate low servicing and production costs.

SUMMARY OF THE INVENTION

It is accordingly an object of the present invention to provide a tankfor a reducing agent, a motor vehicle having a tank for a reducing agentand a method for operating an SCR system of a motor vehicle, whichovercome the hereinafore-mentioned disadvantages and at least partiallysolve the problems of the heretofore-known devices and methods of thisgeneral type. In particular, it is an object to specify a tank for areducing agent, in which the tank permits retroactive installation intoa motor vehicle. It is also intended to specify a motor vehicle which atleast partially solves the problems highlighted in the introduction andin particular specifies the configuration of a tank for a reducingagent, in which the configuration does not restrict the user with regardto the visibility of the body of the vehicle. Furthermore, it isintended to specify a method for operating an SCR system of a motorvehicle, in which the method permits simple operation of the SCR systemand therefore permits considerable advantages with regard to servicing,production, operating costs and energy consumed.

With the foregoing and other objects in view there is provided, inaccordance with the invention, a tank for a reducing agent formingammonia or including ammonia. The tank comprises a planar first tankvolume having a first height, a first mean base area and a first ratioof the first mean base area to the first height of greater than 500 cm,in particular 1,000 cm or even greater than 1,500 cm. At least oneelongate second tank volume has a second height and a second mean basearea. The at least one elongate second tank volume projects, protrudesor overhangs relative to the planar first tank volume.

It is, of course, possible to use a tank of this type to store areducing agent which already includes ammonia and/or an ammoniaprecursor. However, in the SCR systems used in this case, an aqueousurea solution is preferable as a reducing agent. The aqueous ureasolution is, for example, available under the trademark AdBlue. In thiscase, the solution is injected, sprayed or vaporized into the exhaustline upstream of an SCR catalytic converter, for example through the useof a dosing pump or an injector. Ammonia (NH₃) and water are generatedfrom the aqueous urea solution in a hydrolysis reaction by using acatalyst (for example which is still outside of the exhaust gas) and/oras a result of contact with the hot exhaust gas. The ammonia which isgenerated in this way may react, in an SCR catalytic converter at acorresponding temperature, with the nitrogen oxides of the exhaust gas.

In this case, the consumption of aqueous urea solution is approximately1% to 8% of the fuel (diesel fuel) which is used, depending on theuntreated emissions of the internal combustion engine. It is thereforenecessary precisely in this case for a correspondingly large tank volumeto be carried on board.

The tank is shaped in such a way that a first tank volume has a planarconstruction, that is to say simultaneously has a comparatively largelength and/or width, while having a small height. The first mean basearea of the first tank volume is generated by averaging the tankcross-sectional area over the first height (that is to sayperpendicularly thereto). In this case, the first height is preferablyalso the greatest height of the first tank volume, which is preferablyfor example a maximum of 10 cm or even only a maximum of 5 cm. Theelongate second tank volume forms a direct continuation of the firsttank volume, and is in particular non-detachably connected to the firsttank volume. In this case, the second tank volume has, along itselongate extent, a second height which is comparatively large inrelation to the length and width of the second tank volume. The secondmean base area is generated, similarly to the first tank volume, byaveraging the tank cross-sectional area of the second tank volume overthe second height. In this case, the second height is preferably theaveraged or even the smallest height of the second tank volume, which ispreferably for example at least 20 cm or even at least 50 cm. The secondtank volume is in particular formed relative to the first tank volume insuch a way that the first height and the second height, and accordinglyalso the first and second mean base areas, extend in each case invirtually the same direction (parallel). The first base area ispreferably at least 0.5 m or even at least 1m².

In accordance with another feature of the invention, the tank ispreferably constructed in such a way that a second ratio of the secondmean base area and the second height is smaller than 2 cm, in particularsmaller than 1.5 cm.

In particular, the ratio of the second height (H2) to the first height(H1) is greater than 3:1, that is to say

$\frac{H\; 2}{H\; 1} > 3.$

If appropriate, the ratio may even be at least 5:1.

In accordance with a further feature of the invention, the at least onesecond tank volume is disposed directly in an edge region of the firsttank volume, and in particular in a corner region of the first tankvolume. In addition to the at least one second tank volume, the tank mayalso have further second tank volumes which are advantageously likewisedisposed in the edge region of the first tank volume, particularlyadvantageously in the further corner regions of the first tank volume.

In accordance with an added feature of the invention, the first tankvolume for holding the reducing agent preferably has a first volume ofat least 90 l (liters) and the at least one elongate second tank volumepreferably has a second volume which encompasses at most 10% of thefirst volume, and in particular at most 5%. If a plurality of elongatesecond tank volumes are to be provided, the respective volume of thesecond tank volumes should in particular be adapted to the number ofsecond tank volumes, that is to say in the case of two second tankvolumes being provided, the respective second volumes are at most 5% ofthe first volume, and in the case of three second tank volumes beingprovided, the respective second volumes are in each case 3.3% of thefirst volume. In particular, the plurality of second tank volumes aredirectly connected to one another through the use of a collecting line,in such a way that the liquids which are contained in the second tankvolumes can be exchanged with one another. In this case, the collectinglines are in particular connected to that end of the second tank volumewhich is disposed so as to face away from the first tank volume.

In accordance with an additional feature of the invention, a third tankvolume is connected through a connecting line to the first tank volumeand/or to the at least one second tank volume. In this case, the thirdtank volume should be matched in terms of its shape to the spatialconditions in the vehicle. The volume of the third tank volume howevercorresponds in particular to that of the at least one second tankvolume, that is to say encompasses for example at most 10% of the firstvolume. According to a further advantageous refinement, the third tankvolume is significantly smaller than the at least one second tankvolume. The third tank volume thus has a third volume which correspondsin particular to at most 1% of the first volume.

In accordance with yet another feature of the invention, the at leastone second tank volume and/or the third tank volume of the tankpreferably includes a heater. In this case, the heater is in particularan electrical heater, which can for example be connected to electricalaccumulators or electrical generators of a motor vehicle. The heatingpower can in particular be automatically activated on demand and/orregulated and should be configured with regard to a maximum heatingpower such that a frozen reducing agent with a volume of a minimum of0.5 l (liters) is liquefied within 10 minutes.

In accordance with yet a further feature of the invention, at least thefirst tank volume has a housing composed of plastic. High-grade steel orplastic tanks are particularly suitable for reducing agents, inparticular for an aqueous urea solution. In the present embodiment ofthe tank, however, plastic is preferable since it has a lower weightthan a construction using high-grade steel and has a certain expansioncapability. It is very particularly preferable in this case to usepolyurethane as a material, for example a high-pressure-resistantpolyurethane. At least the first tank volume of the tank has heatinsulation. The heat insulation is in particular constructed so as toencompass only a partial region of the first tank volume.

With the objects of the invention in view, there is also provided amotor vehicle, comprising an internal combustion engine, an exhaustsystem having an SCR catalytic converter and a reducing agent meteringdevice, a body with a roof, and a tank, in particular a tank accordingto the invention, disposed on the roof and having a planar first tankvolume for a reducing agent.

The reducing agent metering device includes, for example, an injector oran injection nozzle and a dosing pump which supplies the reducing agentfrom a tank volume to the exhaust system.

The body of the motor vehicle includes all of the structural parts ofthe motor vehicle and a roof which is disposed above a driver's cab. Theplanar first tank volume is disposed on the roof, in particular in sucha way that a driver or user (that is to say any other persons present inthe driver's cab) of the vehicle is not restricted in terms of theirfreedom of movement by the first tank volume. In particular, the firsttank volume may be disposed above the roof, below the roof or elsewithin the roof. The first tank volume may have cutouts or otherprofiles which are adapted firstly to the construction of the roofand/or to the freedom of movement of the driver or user. In this case,the tank preferably extends over virtually the entire area of the roofand therefore, through the use of the largest possible base area and thesmallest possible height, utilizes the greatest possible first tankvolume. Likewise, any other desired shape of the first tank volumeequally falls within the scope of this construction of the vehicleaccording to the invention in this case.

In accordance with another feature of the invention, the tank of themotor vehicle preferably has a planar first tank volume and at least oneelongate second tank volume. The at least one elongate second tankvolume is formed so as to project, protrude or overhang in relation tothe planar first tank volume and the at least one second tank volume isdisposed along a roof beam of the body. The first tank volume is thusdistinguished in particular in that the greatest possible length andwidth of the tank are provided so as to utilize the roof area, and thesmallest possible first height is provided in such a way that, as far aspossible, the user or the driver is not restricted. The at least oneelongate second tank volume has the smallest possible width and length,but has a large height along the elongate extent of the second tankvolume, in such a way that the at least one second tank volume can runalong a roof beam of the body. Through the use of as narrow aconstruction of the second tank volume as possible, which is possiblyalso profiled, it is sought firstly to provide a sufficiently largevolume in the second tank volume, and secondly to provide that thefreedom of movement of the user and/or driver is as far as possible notrestricted, and that a reduction of the visibility of the body of thevehicle is avoided as far as possible. In this case, the second tankvolume should be disposed geodetically (with regard to its heightposition) below the first tank volume.

It may thus also be possible, for example, for the first tank volumeand/or the second tank volume to be an integral part of the body and/orof a driver's cab. This applies in particular to applications in whichthe tank is already installed during the production of the motorvehicle. In this connection, “integral” means in particular that thefirst tank volume and/or the second tank volume can be removed with(partial) deformation and/or destruction of the body.

In accordance with a further feature of the invention, a third tankvolume is connected through a connecting line to at least one secondtank volume or to the first tank volume, and at least the first tankvolume is connected through the third tank volume to a reducing agentmetering device.

A second tank volume therefore need not necessarily be provided in thiscase. The third tank volume is thus supplied with the reducing agentdirectly from the first tank volume. The third tank volume is disposedin particular outside the driver's cab, in the vicinity of the dosingpump or of an injector of the reducing agent metering device. The thirdtank volume is in particular disposed in such a way that the waste heatof the engine or the exhaust line can be utilized as heating power forthe third tank volume. Accordingly, the third tank volume is inparticular at least partially heat-insulated with respect to theenvironment, in such a way that freezing of the reducing agent isprevented, or thawing of the reducing agent is accelerated.

The third tank volume is preferably disposed geodetically below the atleast one second tank volume and may, in the case of a plurality ofsecond tank volumes, be connected to each of the plurality or preferablyto a collecting line which connects the plurality of second tankvolumes. The collecting line is preferably connected to those ends ofthe second tank volumes which face away from the first tank volume.

The third tank volume is in particular disposed outside a driver's cabof the motor vehicle, in particular in the direct vicinity of a deliverypump of the SCR system for the reducing agent. If a third tank volume isnot provided, the at least one second tank volume is connected through aconnecting line (which, if appropriate, is flexible, for example formedby a hose) to a reducing agent metering device. The connecting line mayalso be connected to a collecting line of the plurality of second tankvolumes, as already described above.

In accordance with an added feature of the motor vehicle of theinvention, a reducing agent metering device is connected to at least onesecond tank volume which can be filled under gravitational force, or toa third tank volume which can be filled under gravitational force. Inthis case, the reducing agent metering device includes, for example, atleast one pump and an injection configuration or an injector and issupplied with the reducing agent from the at least one second tankvolume or from the third tank volume. In this case, the at least onesecond tank volume is filled with reducing agent from the first tankvolume as a result of gravitational force. The third tank volume isfilled with reducing agent either from the first tank volume and/or fromthe at least one second tank volume. Such a configuration of the tankvolumes makes it possible to dispense with additional supply pumps, andalso to prevent insufficient filling of a tank volume as a result of themotor vehicle traveling long distances in (oblique) awkward positions.This is obtained in particular by providing a further second tank volumeor the third tank volume, wherein the second tank volumes canadditionally be connected to one another through the use of a collectingline for the equalization of the second tank volumes.

In accordance with an additional feature of the motor vehicle of theinvention, a roof region of the motor vehicle has heat insulation, suchthat at least the first tank volume of the tank is at least partiallyinsulated with respect to the external environment by the heatinsulation. In this case, the (in particular non-metallic) heatinsulation serves in particular to protect the first tank volume fromclimatic influences of the environment, such that freezing of thereducing agent within the first tank volume is prevented as far aspossible, but at the same time a liquefaction of the reducing agent canbe accelerated as a result of the first tank volume not beingheat-insulated with respect to the interior space of the cabin of themotor vehicle.

With the objects of the invention in view, there is concomitantlyprovided a method for operating an SCR system of a motor vehicle havingat least two tank volumes, a reducing agent metering device and an SCRcatalytic converter. The method comprises storing a reducing agent forthe SCR system in one of the tank volumes,

during operation of the motor vehicle, automatically filling at leastone further of the tank volumes with the reducing agent from the onetank volume, and forming a reservoir for the reducing agent meteringdevice with the at least one further tank volume. The method is proposedin particular for operating a motor vehicle according to the invention,and the motor vehicle has in particular a tank according to theinvention.

It is also the case herein that the reducing agent metering deviceincludes for example an injector or a delivery pump and an injectionnozzle for dispensing the reducing agent into the exhaust line. Themethod is distinguished in that, during the operation of the motorvehicle, the reducing agent is delivered from a first tank volume intoat least one further tank volume as a result of gravitational force, insuch a way that the at least one further tank volume forms an inparticular permanently-filled reservoir for the reducing agent meteringdevice. A reservoir therefore refers to a volume which is permanentlyfilled in particular in awkward positions of the vehicle and when thefurther tank volumes which are provided are partially filled, and whichcan be emptied through the reducing agent metering device only once thefurther tank volumes have emptied.

Other features which are considered as characteristic for the inventionare set forth in the appended claims, noting that the features specifiedindividually in the dependent claims may be combined with one another inany desired technologically expedient manner, and define furtherrefinements of the invention. Although the invention is illustrated anddescribed herein as embodied in a tank for a reducing agent, a motorvehicle having a tank for a reducing agent, and a method for operatingan SCR system of a motor vehicle, it is nevertheless not intended to belimited to the details shown, since various modifications and structuralchanges may be made therein without departing from the spirit of theinvention and within the scope and range of equivalents of the claims.

The construction and method of operation of the invention, however,together with additional objects and advantages thereof will be bestunderstood from the following description of specific embodiments whenread in connection with the accompanying drawings.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWING

FIG. 1 is a diagrammatic, perspective view of a tank;

FIG. 2 is a side-elevational view of a vehicle having a tank;

FIG. 3 is a diagrammatic and schematic view showing details of a motorvehicle which are important to the invention; and

FIG. 4 is a view similar to FIG. 3 showing a further view of details ofa motor vehicle which are important to the invention.

DETAILED DESCRIPTION OF THE INVENTION

Referring now in detail to the figures of the drawings, which showparticularly preferred embodiment variants of the invention, without theinvention being restricted thereto and first, particularly, to FIG. 1thereof, there is seen a diagrammatic, perspective view of a tank 1having a housing 17 and a first tank volume 3 with a first mean basearea GF1, a first height H1 and a corresponding first volume V1. Thefirst tank volume 3 is connected to a second tank volume 7 of the tank 1having a second mean base area GF2, a second height H2 and acorresponding second volume V2. In this case, the second tank volume 7is disposed in an edge region 21 of the first tank volume 3. The tank 1,in this case, may also have further second tank volumes 7 which, ifappropriate, are connected to one another through the use of acollecting line 23 that is connected to those ends of the second tankvolumes 7 which face away from the first tank volume 3. The collectingline 23, or the at least one second tank volume 7, is connected througha connecting line 10 to a reducing agent metering device 13, through theuse of which a reducing agent 2 is supplied to an exhaust system 14,seen in FIGS. 2, 3 and 4. Furthermore, if appropriate, the second tankvolumes 7 have a heater 16 which is preferably disposed in the region ofa tank outlet 24 of the second tank volume 7.

FIG. 2 is a diagrammatic side view which shows a motor vehicle 5 with anexhaust system 14 and a body 22 with a roof 6 and a roof beam 8. In thiscase, a tank 1 for a reducing agent 2 has a first tank volume 3 disposedin a roof region 4 of the motor vehicle 5.

FIG. 3 diagrammatically shows details of a motor vehicle 5 which areimportant to the invention, in particular an internal combustion engine15 with an exhaust system 14 connected thereto, in which the exhaustsystem 14 includes at least one SCR catalytic converter 11. The reducingagent 2 is supplied from a first tank volume 3 of a tank 1 and from asecond tank volume 7 through a connecting line 10 to a reducing agentmetering device 13, which supplies the reducing agent 2 to the exhaustsystem 14 through an injection configuration or an injector. In thisembodiment, an SCR system 19, denoted in FIG. 3 by a dashed line,includes at least the two tank volumes, that is the first tank volume 3and the second tank volume 7, as well as the reducing agent meteringdevice 13 and the SCR catalytic converter 11. The tank 1 is disposedwith its first tank volume 3 in the region of the roof 6 and is inparticular at least partially integrated into the roof, with the housing17 of the tank 1, in particular of the first tank volume 3, being atleast partially insulated with respect to the external environmentthrough the use of heat insulation 18. The second tank volume 7 extendsdownward from an edge region 21 of the first tank volume 3 along a roofbeam 8, and has, at its lower end, a tank outlet 24, in the vicinity ofwhich a heater 16 is disposed if appropriate.

FIG. 4 diagrammatically shows a further view of details of a motorvehicle 5 which are relevant to the invention. In this case, similarlyto FIG. 3, a tank 1 is disposed with its first tank volume 3 in a roof 6of a motor vehicle 5 and extends downward with a second tank volume 7along a roof beam 8. The second tank volume 7 is connected through aconnecting line 10 to a third tank volume 9 which, if appropriate, has aheater 16 within the third tank volume 9 in the vicinity of a tankoutlet 24. The reducing agent 2 is metered to the exhaust system 14upstream of an SCR catalytic converter 11 from the third tank volume 9through the use of a reducing agent metering device 13. In this case,the third tank volume 9 serves as a reservoir 20 for the reducing agentmetering device 13. In particular, the reservoir 20 is supplied with thereducing agent 2 from the other tank volumes (3, 7) under gravitationalforce 12, in such a way that all of the other tank volumes (3, 7) areemptied before the reservoir 20.

1. A tank for a reducing agent forming ammonia or including ammonia, thetank comprising: a planar first tank volume having a first height, afirst mean base area and a first ratio of said first mean base area tosaid first height of greater than 500 cm; and at least one elongatesecond tank volume having a second height and a second mean base area,said at least one elongate second tank volume projecting relative tosaid planar first tank volume.
 2. The tank according to claim 1, whereina second ratio of said second mean base area to said second height issmaller than 2 cm.
 3. The tank according to claim 1, wherein said firsttank volume has an edge region, and said at least one second tank volumeis disposed directly in said edge region of said first tank volume. 4.The tank according to claim 1, wherein said first tank volume has afirst volume of at least 90 liters for holding the reducing agent, andsaid at least one elongate second tank volume has a second volumeencompassing at most 10% of said first volume.
 5. The tank according toclaim 1, which further comprises a third tank volume, and a connectingline connected between said third tank volume and at least one of saidfirst tank volume or said at least one second tank volume.
 6. The tankaccording to claim 5, wherein at least one of said at least one secondtank volume or said third tank volume includes a heater.
 7. The tankaccording to claim 1, wherein at least said first tank volume has ahousing composed of plastic.
 8. The tank according to claim 1, whereinat least said first tank volume has heat insulation.
 9. A motor vehicle,comprising: an internal combustion engine; an exhaust systemcommunicating with said internal combustion engine and having an SCRcatalytic converter and a reducing agent metering device; a body with aroof; and a tank disposed on said roof, communicating with said exhaustsystem and having a planar first tank volume for a reducing agent. 10.The motor vehicle according to claim 9, wherein said body has a roofbeam, and said tank has at least one elongate second tank volume, saidat least one elongate second tank volume being disposed along said roofbeam and projecting relative to said planar first tank volume.
 11. Themotor vehicle according to claim 10, which further comprises a thirdtank volume, and a connecting line connected between said third tankvolume and at least one of said at least one second tank volume or saidfirst tank volume, at least said first tank volume being connectedthrough said third tank volume to said reducing agent metering device.12. The motor vehicle according to claim 10, wherein said reducing agentmetering device is connected to said at least one second tank volumewhich can be filled under gravitational force.
 13. The motor vehicleaccording to claim 11, wherein said reducing agent metering device isconnected to said third tank volume which can be filled undergravitational force.
 14. The motor vehicle according to claim 9, whichfurther comprises a roof region having heat insulation, at least saidfirst tank volume of said tank being at least partially insulated bysaid heat insulation.
 15. A method for operating an SCR system of amotor vehicle having at least two tank volumes, a reducing agentmetering device and an SCR catalytic converter, the method comprisingthe following steps: storing a reducing agent for the SCR system in oneof the tank volumes; during operation of the motor vehicle,automatically filling at least one further of the tank volumes with thereducing agent from the one tank volume; and forming a reservoir for thereducing agent metering device with the at least one further tankvolume.